OK, finally had a chance to get a look again at this today. To answer your question Nino - yes i have tested mini pf movement with it installed in the machine - no areas of binding.

Taking a look from the beginning again, i tested continuity from the motor driver board to J122 on the power driver board - all good, and motor driver board light is on.  The voltage is around 9V at the motor driver board - is this a bit low?
 The thing that confuses me is that the manual and the tech chart show different wire colours for J122 - ie: manual in section 3 states pin3 is blue vellow, but tech chart shows blue yellow as pin 4!!! I swapped these around, no difference though.

BUT i am trying to get the motor to drive by grounding the transistor. I assume from this http://www.pinballrebel.com/pinball/cards/Tech_Charts/Bally_Doctor_Who_Tech_Chart.pdf that Q22 is the correct one?  When i ground it, nothing happens. Also, i am not sure of the function of Q20 (mini pf on/off) - do both need to be grounded together?  Q20 grounding by itself does nothing as well.

Thanks in advance